What are the key immunologic parameters which control the amplification and progression of the autoimmune response in IDDM? We believe that the means are now at hand to identify the specific molecular and cellular mechanisms which underlie these events, and to directly evaluate their impact on the rate of progression to IDDM in human populations. This program project brings together an interdisciplinary range of expertise in bioengineering, cellular and molecular immunology, endocrinology, and genetics, to address this question with four closely interrelated projects and three Cores: Project 1 will identify and manipulate specific topographical elements within the HLA-DQ peptide-binding groove which dictate peptide orientation, conformation, and affinity for peptide-HLA combinations associated with IDDM, using a blend of molecular modeling, expression and mutagenesis, and peptide binding studies. Project 2 will quantitate T cell precursors in pre-diabetics with specificity for IDDM- associated autoantigens, and characterize epitope recognition, frequency, and phenotype as well as TCR clonotypes coincident with disease progression; antigen-specific T cells cloned in this project will be used in functional analysis studies in projects 1, 3, and 4. Project 3 will test the hypothesis that macrophages play a key role in the processing of islet cell antigens and specifically in the initial generation of immunodominant peptides associated with the initiation of IDDM. Project 4 will test the hypothesis that newly arising autoantibody-producing B cells in early IDDM contribute to epitope spreading in the T cell compartment by the uptake of antigens associated with IDDM and subsequent HLA-dependent presentation of processed peptides to T cells, with fine specificity influenced by the nature of the B cell autoantibody specificity. The clinical component of this program project is central to all of the research questions being addressed. We will utilize the existing expertise of the diabetes prediction programs of the Diabetes Centers of the University of Washington and Virginia Mason Medical Center to identify and recruit individuals for this program project study. interrelationships among these program objectives will lead to a coordinated research plan utilizing shared resources to achieve a comprehensive perspective on the diabetogenic pathway from initiating events through amplification. These studies will identify clinical opportunities for new approaches to identification and management of the pre-diabetic individual, as well as new therapeutic targets.